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541.
Michael G. Janech Holly A. Gefroh Emily E. Cwengros James A. Sulikowski David W. Ploth Wayne R. Fitzgibbon 《Marine Biology》2008,153(6):1173-1179
One of the two phloretin-sensitive, facilitated urea transporters identified from the kidneys of the myliobatiform, euryhaline
elasmobranch, Dasyatis sabina, a 379 amino acid protein ([D. sabina]strUT-2), was very similar to the 380 amino acid isoform (shUT) present in the kidney of the squaliform, dogfish shark, Squalus acanthias (a species that can be considered marginally euryhaline since it utilizes upper estuarine, as well as ocean habitats). To
test the proposal that this isoform is a conserved urea transporter (UT) expressed in the kidneys of diverse elasmobranchs,
UTs were cloned from the kidneys of a rajiform elasmobranch, the stenohaline skate, Leucoraja ocellata and another dasyatid stingray, the marginally euryhaline, Dasyatis say. Utilizing 5′/3′ RACE, a 2,060 nt cDNA that encoded a phloretin-sensitive, 378 amino acid skate urea transporter ([L. ocellata]skUT-2) and a 1,683 nt cDNA that encoded a stingray 379 amino acid UT ([D. say]strUT-2) were obtained. These deduced UTs have a very high sequence identity with the known elasmobranch Uts. [L. ocellata]skUT-2 was 86% identical to [D. sabina]strUT-2 and 84% identical to [S. acanthias]shUT. [D. say]strUT-2 was 97% identical to the [D. sabina]strUT-2. These findings support the hypothesis that a conserved UT isoform is present in the kidneys of marine elasmobranchs,
and is an important pathway for facilitated urea transport in the kidneys of marine elasmobranchs.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
H.A. Gefroh and E.E. Cwengros contributed equally to this study. 相似文献
542.
Christopher M. Brown James D. MacKinnon Amanda M. Cockshutt Tracy A. Villareal Douglas A. Campbell 《Marine Biology》2008,154(3):413-422
Phytoplankton function and acclimation are driven by catalytic protein complexes that mediate key physiological transformations,
including generation of photosynthetic ATP and reductant, and carbon and nitrogen fixation. Quantitation of capacities for
these processes allows estimation of rates for key ecosystem processes, and identification of factors limiting primary productivity.
We herein present molar quantitations of PSI, PSII, ATP synthase, RuBisCO and the Fe protein of nitrogenase of Trichodesmium collected from the Gulf of Mexico, in comparison to determinations for a range of cyanobacteria growing in culture. Using
these measurements, estimates were generated for Trichodesmium capacities for carbon fixation of 1–3.4 g C g chl a
−1 h−1 and nitrogen fixation of 0.06–0.17 g N g chl a
−1 h−1, with diel variations in capacities. ATP synthase levels show that ATP synthesis capacity is sufficient to support these
levels of carbon and nitrogen fixation, and that ATP synthase levels change over the day in accordance with the ATP demands
of nitrogenase and RuBisCO activity. Levels of measured complexes indicate that Trichodesmium manifests n-type diel light acclimation through rapid changes in RuBisCO:PSII, supported by significant investment of cellular nitrogen.
The plasticity in the levels and stoichiometry of these core complexes show that changes in the abundance of core protein
complexes are an important component of acclimation and regulation of metabolic function by Trichodesmium populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
543.
James D. McCleave 《Marine Biology》2008,155(3):249-262
This study reviewed literature on spawning times for three north temperate species of anguillid eels estimated by sampling
for small leptocephali (larvae) at sea and for several temperate and tropical species by back-calculating from putative daily
ages derived from otolith increment analysis of glass eels that recruited to coastal waters. Estimates from otoliths of European
eels, Anguilla anguilla, American eels, Anguilla rostrata, and Japanese eels, Anguilla japonica, imply much more protracted spawning seasons than are indicated by sampling at sea during various times of year. European
eels are inferred to spawn year-round from otolith analysis, but the smallest, recently hatched leptocephali are found only
in late winter and spring. From otoliths, the spawning times of these three species are all estimated to occur much later
in the year than when small leptocephali are found at sea, indicating that ages appear to be underestimated. For these and
other temperate and tropical eels, there are inconsistencies in assigned ages among various studies, which are most extreme
for the European eel. This species has the longest larval migration and often has an opaque zone in the glass eels’ otoliths
where it is difficult to discern growth increments. These inconsistencies suggest that interpretation of otolith growth increments
is incorrect at least in some studies, and the apparently consistent mismatch between otolith and sea-sampling studies suggests
that increments may not always be formed at some period during the unusual early life history of anguillids. Because daily
increments may be formed in eels during most of their early life history, future research is needed to determine the cause
of the mismatch of glass eel aging studies and the apparent spawning times of eels offshore.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
James D. McCleaveEmail: |
544.
Chemical and colloidal analyses of natural seep water collected from the exploratory studies facility inside Yucca Mountain,Nevada, USA 总被引:1,自引:0,他引:1
Cizdziel JV Guo C Steinberg SM Yu Z Johannesson KH 《Environmental geochemistry and health》2008,30(1):31-44
Yucca Mountain is being considered as a geological repository for the USA’s spent nuclear fuel and high-level nuclear waste.
Numerous groundwater seeps appeared during March 2005 within the exploratory studies facility (ESF), a tunnel excavated in
the mountain. Because of the relevance to radionuclide transport and unsaturated zone-modeling studies, we analyzed the seep
samples for major anions and cations, rare earth elements, and colloids. Major ion species and elemental concentrations in
seep samples reflect interaction of the water with the volcanic rock and secondary calcites. Elemental fractograms from flow-injection
field-flow fractionation ICP–MS scans detected Br, Ca, Cl, Cu, Fe, I, Mg, Si, Sr, W, and U at void fractions, suggesting they
may be present in the form of dissolved anions. Colloids approximately 10 nm in hydrodynamic diameter, possibly calcite, were
also present in the seepage samples. Geochemical calculations indicate, however, these may be an artifact (not present in
the groundwater) which arose because of loss of CO2 during sample collection and storage. 相似文献
545.
Polymorphism frequently correlates with specialized labor in social insects, but extreme morphologies may compromise behavioral
flexibility and thus limit caste evolution. The ant genus Pheidole has dimorphic worker subcastes in which major workers appear limited due to their morphology to performing defensive or trophic
functions, thus providing an ideal model to investigate specialization and plasticity. We examined worker morphology, brood-care
flexibility, and subcaste ratio in 17 species of tropical twig-nesting Pheidole by quantifying nursing by major workers in natural colonies and in subcolonies lacking minors, in which we also measured
brood survival and growth. Across species, majors performed significantly less brood care than minors in intact colonies,
but increased rates of brood care 20-fold in subcolonies lacking minors. Brood nursed by majors had lower survival than brood
tended by minors, although rates of brood growth did not vary between subcastes. Significant interspecific variation in rates
of brood care by major workers did not lead to significant differences in brood growth or survival. Additionally, we did not
find a significant association between the degree of major worker morphometric specialization and rates of nursing, growth,
or survival of brood among species. Therefore, major workers showed reduced efficacy of brood care, but the degree of morphological
specialization among species did not directly compromise task plasticity. The compact nests and all-or-nothing consequences
of predation or disturbance on colony fitness may have influenced the evolution of major worker brood-care competency in twig-nesting
Pheidole.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Dedicated to Professor Edward O. Wilson on the occasion of his 80th birthday. 相似文献
546.
Megalopae of several crab species exhibit active habitat selection when settling. These megalopae usually select structurally
complex habitats which can provide refuge and food. The portunid mud crab, Scylla serrata, is commonly found within the muddy estuaries of the Indo-West Pacific after attaining a carapace width >40 mm. Despite substantial
efforts, the recruitment mechanism of juvenile mud crabs to estuaries is not understood because their megalopae and early
stage crablets (carapace width <30 mm) are rarely found. We used laboratory experiments to determine whether megalopae and
early stage crablets are selective among three estuarine habitats which commonly occur in Queensland, Australia. These animals
were placed in arenas where they had a choice of habitats: seagrass, mud or sand, and arenas where they had no choice. Contrary
to the associations exhibited by other portunid crab megalopae, S. serrata megalopae were not selective among these estuarine habitats, suggesting that they tend not to encounter these habitats, or,
gain no advantage by selecting one over the others. The crablets, however, strongly selected seagrass, suggesting that residing
within seagrass is beneficial to the crablets and likely increases survival. This supports the model that for S. serrata, crablets and not megalopae tend to colonise estuaries, since a selective behaviour has evolved within crablets but not megalopae. 相似文献
547.
Network structure and parasite transmission in a group living lizard,the gidgee skink, <Emphasis Type="Italic">Egernia stokesii</Emphasis> 总被引:1,自引:1,他引:0
Stephanie S. Godfrey C. Michael Bull Richard James Kris Murray 《Behavioral ecology and sociobiology》2009,63(7):1045-1056
Gidgee skinks (Egernia stokesii) form large social aggregations in rocky outcrops across the Flinders Ranges in South Australia. Group members share refuges
(rock crevices), which may promote parasite transmission. We measured connectivity of individuals in networks constructed
from patterns of common crevice use and observed patterns of parasitism by three blood parasites (Hemolivia, Schellackia and Plasmodium) and an ectoparasitic tick (Amblyomma vikirri). Data came from a 1-year mark-recapture study of four populations. Transmission networks were constructed to represent possible
transmission pathways among lizards. Two lizards that used the same refuge within an estimated transmission period were considered
connected in the transmission network. An edge was placed between them, directed towards the individual that occupied the
crevice last. Social networks, a sub-set of same-day only associations, were small and highly fragmented compared with transmission
networks, suggesting that non-synchronous crevice use leads to more transmission opportunities than direct social association.
In transmission networks, lizards infested by ticks were connected to more other tick-infested lizards than uninfected lizards.
Lizards infected by ticks and carrying multiple blood parasite infections were in more connected positions in the network
than lizards without ticks or with one or no blood parasites. Our findings suggest higher levels of network connectivity may
increase the risk of becoming infected or that parasites influence lizard behaviour and consequently their position in the
network.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and
R. James). 相似文献
548.
Douglas G. Sprugel Katherine G. Rascher Rolf Gersonde Martin Dovčiak James A. Lutz Charles B. Halpern 《Ecological modelling》2009
Young forests can be manipulated in diverse ways to enhance their ecological values. We used stem maps from two dense, second-growth stands in western Washington and a spatially explicit light model (tRAYci) to simulate effects of five silvicultural manipulations on diameter distribution, species composition, spatial patterning, and light availability. Each treatment removed 30% of the basal area, but differed in how trees were selected for removal. Three primary treatments were thin from below (removing the smallest trees), random thin (removing trees randomly), and gap creation (removing all trees in circles ∼1 tree height in diameter). Two additional treatments combined elements of these approaches: random ecological thin (a mixture of thin from below and random thin) and structured ecological thin (a mixture of thin from below and gap creation). 相似文献
549.
Strike propensities refer to the extent to which union members are willing to engage in strikes. The present paper identifies four motivational explanations for individual propensity to strike: social exchange relationships between member and union, and member and company, economic circumstances, and social status. These four models complement each other, and together permit substantial integration of previous literature as well as suggesting new antecedents of strike propensities. We evaluated each model using survey data from 2548 unionized retail employees. While the economic model explained the most variance in strike propensity, each model accounted for a significant amount of unique variation in the members' strike propensities. Our organizational framework of the motivational explanations of strike propensity into four distinct but complementary motivational models and our addition of new predictor variables represent our study's major contributions. Implications for strike research and union member–union relations are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
550.
Hillol Guha James E. Saiers Scott Brooks Phil Jardine Krishnaswamy Jayachandran 《Journal of contaminant hydrology》2001,49(3-4):311-334
We examine how the processes of advection, dispersion, oxidation-reduction, and adsorption combine to affect the transport of chromium through columns packed with pyrolusite (beta-MnO2)-coated sand. We find that beta-MnO2 effectively oxidizes Cr(III) to Cr(VI) and that the extent of oxidation is sensitive to changes in pH, pore water velocity, and influent concentrations of Cr(III). Cr(III) oxidation rates, although initially high, decline well before the supply of beta-MnO2 is depleted, suggesting that a reaction product inhibits the conversion of Cr(III) to Cr(VI). Rate-limited reactions govern the weak adsorption of each chromium species, with Cr(III) adsorption varying directly with pH and Cr(VI) adsorption varying inversely with pH. The breakthrough data on chromium transport can be matched closely by calculations of a simple model that accounts for (1) advective-dispersive transport of Cr(III), Cr(VI), and dissolved oxygen, (2) first-order kinetics adsorption of the reduced and oxidized chromium species, and (3) nonlinear rate-limited oxidation of Cr(III) to Cr(VI). Our work supplements the limited database on the transport of redox-sensitive metals in porous media and provides a means for quantifying the coupled processes that contribute to this transport. 相似文献